JPH0821741A - Object sensor - Google Patents

Abstract

PURPOSE:To provide an object sensor in which an erroneous operation due to environmental changes such as a temperature, a humidity, etc., does not occur. CONSTITUTION:The object sensor has a capacity change type converter 4 having a sensor electrode 5 and a shielding case 6, and comprises an oscillator 1 in which its output is varied in response to the change of an electrostatic capacity due to the approach or the separation of an object, a peak value detector for holding the peak value of the output of the oscillator 1, a high-pass filter, an output discriminator 2 which has an AC amplifier and in which an output is not changed when the output of the oscillator 1 slowly changes and the output is changed when it relatively fast changes, and an output circuit 3 for converting the output of the discriminator 2 into a pulselike output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting the proximity or separation of a human body or an object.

More specifically, the present invention relates to an object detection device that utilizes a change in electrostatic capacitance due to the proximity or separation of a human body or an object.

[0003]

2. Description of the Related Art Conventionally, as an object detecting device, a real object was a Shoko 63.
There is one as shown in Japanese Patent No. 36246.

This is because the detection electrode is connected to a pulse delay circuit, and when the object approaches the detection electrode, the delay time of the pulse changes due to the change in the capacitance between the detection electrode and the ground and exceeds the reference delay time. The output signal is sometimes inverted.

[0005]

The conventional one has the advantage that the output signal maintains the inverted state if the object is within the detection distance range of the detection device, but the performance is large due to changes in ambient temperature or humidity. It had the problem of fluctuating.

[0006] That is, when the temperature and humidity change, the detection distance changes, the output signal is inverted when there is no object at the time of unavailability, and the output signal does not invert even when the object is brought close to the detection device. There was an occasion. In addition, the output signal may be inverted when the temperature suddenly changes and dew condensation occurs.

An object of the present invention is to solve the above problems and to provide an object detection device which reliably detects the proximity of an object without malfunctioning even if there is a change in temperature and humidity or dew condensation.

[0008]

In order to solve the above-mentioned problems, the present invention includes a capacitance change type converter comprising a sensor electrode and a shield case, and responds to a change in capacitance due to proximity or separation of an object. An oscillator in which the output changes, an output discriminating circuit in which the output does not change in response to a relatively slow change in the output of the oscillator, and an output changes in response to a relatively fast change, and the output of the output discriminating circuit An output circuit is provided for converting the output voltage to a predetermined voltage or pulse width output.

Further, the first output for generating an output pulse having a predetermined voltage and pulse width when the proximity of the object is detected so that it can be distinguished whether the object is approaching the object detecting device or separating from the object detecting device. A circuit and a second output circuit for generating an output pulse having a predetermined voltage and pulse width when the separation of the object is detected are provided. Furthermore, like the conventional example,
If the object is within the detection distance range of the detection ground device, the output signal is maintained in the inverted state, and an output pulse that rises when the proximity of the object is detected and falls when the separation of the object is detected is generated. 3 output circuits are provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the embodiments shown in the accompanying drawings.

FIG. 1 shows a circuit diagram of a first embodiment of the present invention. In FIG. 1, TR1 to TR3 are transistors and C
1 to C9 are capacitors, R1 to R17 are resistors, VR1 to
VR2 is a variable resistor, Q1 to Q2 are amplifiers such as operational amplifiers, and D1 is a diode. + V is a power source, GN
D is the ground.

Reference numeral 4 denotes a variable capacitance converter (hereinafter referred to as a converter) in which a capacitor is constituted by a sensor electrode 5 made of a conductive member and a shield case 6 made of a conductive member. In order to clarify the configuration of the converter 4, the configuration of the object detection device of the present invention will be described with reference to FIG.

Reference numeral 10 denotes a circuit board constituting the circuit of FIG. 1, which is fixed in a metal box-shaped shield case 6. The shield case 6 is electrically connected to a predetermined place in the circuit.

The shield case 6 forms an electrostatic capacity between the shield case 6 and the sensor electrode 5, and also serves to prevent external noise from entering the sensor electrode 5 and the circuit.

The sensor electrode 5 is fixed to the circuit board 10 at a predetermined distance by a plurality of legs 5b, and is electrically connected to the circuit.

The end portion 5a of the sensor electrode 5 and the end portion 6a of the shield case 6 are arranged at an appropriate distance in consideration of the object detection performance. In FIG. 2, the upper surface of the sensor electrode 5 and the upper surface of the end 6a of the shield case 6 are the same surface, but they may not be the same, and a step may be provided depending on the detection performance. Further, in some cases, the shield case may not be formed in a box shape, but a simple metal plate may be provided so as to face the sensor electrode 5. The shield case 6 is fixed to a case 8 made of plastic or the like by a known method, and is sealed by a back cover 9.

The detection area AR for detecting an object generally becomes narrower with distance from the sensor electrode, as shown by the dotted line in the figure.

Reference numeral 1 denotes a Wien bridge type oscillator whose output changes due to a change in electrostatic capacitance caused by an object moving toward or away from the converter 4. The output waveform (frequency and voltage) P1 is determined by the resistance value of the resistor R5, the variable resistor VR1 and the capacitance value of the capacitor C2. Here, the converter 4 is further connected between the base and emitter of TR3. Yes, the output voltage (P1) changes when the electrostatic capacitance of the converter 4 changes when an object approaches. In addition, the shield case 6 of the converter 4 may be connected to GND. Since the voltage between the base and the emitter is substantially constant, by connecting the converter 4 between the base and the emitter, the capacitance of the converter 4 can be ignored in the steady state. Therefore, since only the capacitance change due to the proximity of the object can be used, a highly sensitive detection device can be constructed. TR1 of the transistor is TR2, R2, R4
Is a transistor for improving the temperature characteristics of the operating point of the amplifier consisting of. The capacitor C1 is for stabilizing the operating point of TR2, and VR1 adjusts the output waveform, that is, the detection sensitivity.

Reference numeral 2 denotes an output discriminating circuit whose output changes in response to a relatively rapid change in the output fluctuation of the oscillator 1. The output discriminating circuit 2 includes a diode D1, resistors R7 to R8, capacitors C3 to C8, and a transistor TR4, and a peak value detection circuit that holds the peak value of the AC waveform in each cycle, a capacitor C5, and resistors R9 to R10. High pass filter consisting of amplifier Q1, resistor R11
.About.R14 and capacitors C6 to C7. C7 is for removing relatively high frequency noise. R13 is to accelerate the charging of the capacitor C42 when the power is turned on, and to shorten the time until the circuit becomes stable.

Reference numeral 3 is an output circuit for converting the output waveform of the output discriminating circuit 2 into a pulse, which includes an amplifier Q2 and resistors R16 to R16.
17, a variable resistor VR2 and a capacitor C9, and a noise removal circuit composed of a resistor R15 and a capacitor C8. Variable resistor V
The threshold value Vth of the comparator can be adjusted by R2. C9 is a capacitor for stabilizing the threshold Vth.

FIG. 3 is a timing chart showing output voltage waveforms (hereinafter referred to as outputs P1 to P6) of P1 to P6 of the circuit of FIG. A period T1 shows an initial steady state in which there is no detected object, and a period T2 shows a time when the object approaches, crosses, or leaves the detection range of the converter 4 at a relatively high speed. The period T3 shows the time when the ambient environment such as temperature and humidity changes gradually, and the period T4 shows the period T2.
The change in the surrounding environment is slower, but faster than the period T3, and the period T5 is in a steady state after the change in the surrounding environment disappears.

The operation will be described below with reference to FIGS.

Since the state does not change in the period T1, the oscillator 1 oscillates at a constant frequency and a constant amplitude, and the output P1 is constant. The output P2 of the peak value detection circuit composed of the diode D1, the resistor R7, and the capacitor C3 becomes a pulsating flow in which high frequency components remain, but the transistor TR
4, the output P3 that has passed through the impedance conversion and smoothing circuit composed of the capacitor C4 and the resistor R8 becomes a substantially constant DC voltage. The impedance conversion circuit outputs P2
This is to prevent the voltage of the device from decreasing. As a result, the output P4 of the high pass filter and the output P5 of the AC amplifier also become constant DC voltage. Since the threshold value Vth of the comparator is set lower than the voltage of the output P5 in the normal state, the output P6 of the comparator is at the GND level.

In FIG. 2, the object 7 moves from the left side of the drawing in parallel with the sensor electrode 5 to reach the detection area AR (see the solid line), crosses it, and leaves the detection area (see the dashed line). Considering the case, the state changes from the period T1 to the period T2 in FIG.

Since the electrostatic capacitance of the converter 4 changes due to the proximity of the object, the output P1 of the oscillator 1 changes. The output P3 also changes accordingly. This change is relatively fast, so
The direct current component is cut by the capacitor C5 that constitutes the high-pass filter, and a differential waveform as shown in the output P4 is obtained. The output P4 is further amplified by the AC amplifier and output P5
However, the output appears at the output P6 only during the period when this voltage exceeds the threshold value Vth of the comparator (the period when it becomes lower than the threshold value Vth in FIG. 3).

In the period T3, the output P1 of the oscillator 1 gradually changes due to changes in the surrounding environment. The output P3 has a DC voltage fluctuation, but this is a slow change and the output P4 does not change. . Therefore, the output P5 does not change, and no output appears at the output P6.

A period T4 is slower than the period T2 but faster than the period T3. In this case, the output P3 also changes, but the change is the period T
Since it is slower than the case of 2, it is a change that cannot be amplified by the high-pass filter and AC amplifier, and the output P5
Does not exceed the threshold value Vth, and no output appears at the output P6.

During the period T5, as in the case of T1, the state does not change, so that no output appears at the output P6.

It is possible to appropriately change how much the state is changed to output the output by setting the circuit constants of the oscillator 1 and the output discrimination circuit 2 or adjusting the threshold value Vth of the comparator of the output circuit 3. Further, the output circuit is not limited to the circuit shown in FIG. 1, but a timer may be provided to output a pulse having a predetermined width, or the like.

FIG. 4 shows a circuit block diagram of the second embodiment.

In FIG. 4, 41 is resistors R41 to R4.
5, a diode D41, a comparator Q41 and the same converter 4 as in the above-mentioned embodiment.
The duty ratio of the output pulse waveform changes due to the change in the electrostatic capacitance due to the approach or separation of the object from the sensor electrode 5. In this circuit, the shield case 6 of the converter 4 is connected to GND.

Reference numeral 42 denotes an output discriminating circuit whose output changes in response to a relatively rapid change in the output of the oscillator 1.
The output discrimination circuit 42 includes a smoothing circuit including a resistor R46 and a capacitor C41, an amplifier Q42, resistors R47 to R51,
And an AC amplifier including capacitors C42 to C43. C43 is for removing relatively high frequency noise. R50 is for speeding up the charging of the capacitor C42 when the power is turned on and for shortening the time until the circuit becomes stable.

Reference numeral 43 is a first output circuit including a comparator, a timer, a waveform shaping circuit and the like. The threshold value Vth2 of the comparator can be adjusted by the variable resistor VR41, and when the output voltage of the output discrimination circuit 42 is higher than the threshold value Vth2, a pulse is output to the output terminal OUT1.

Similarly, 44 is a comparator, a timer,
It is a second output circuit including a waveform shaping circuit and the like. The threshold value Vth3 of the comparator can be adjusted by the variable resistor VR42, and the output voltage of the output discrimination circuit 42 is the threshold value Vt.
When it is lower than h3, a pulse is output to the output terminal OUT2.

FIG. 5 is a timing chart showing output voltage waveforms (hereinafter referred to as outputs P41 to P46) of P41 to P46 of the circuit of FIG. The period T41 indicates an initial steady state in which there is no detected object, and the period T42 is such that the object approaches or crosses the detection range of the converter 4 at a relatively high speed.
The time T43 indicates a steady state after there is no change in the surrounding environment.

When the object approaches the sensor electrode 5 (point tA in FIG. 5), the capacitance of the converter 4 changes and the duty ratio of the pulse of the output P41 of the oscillator 41 decreases, so that the output P42 of the output P42 is reduced by the smoothing circuit. The voltage decreases. The output P43 has a differential waveform in which only the voltage change of the output P42 is taken out by the capacitor C42. This is amplified by the amplifier, and eventually the output P44 of the AC amplifier becomes a voltage change that rises above the normal voltage level and returns to the original level. At this time, if the voltage of the output P44 becomes equal to or higher than the threshold value Vth2, the first
An output P45 having a predetermined width can be obtained from the output circuit of.

On the contrary, when the object is separated from the sensor electrode 5 (point tB in FIG. 5), the electrostatic capacitance of the converter 4 changes and the duty ratio of the pulse of the output P41 of the oscillator 41 returns to the original value. Voltage returns to the original state and becomes the differential waveform P43 in which only the voltage change of the output P42 is extracted. As in the case of the approach, this is amplified by the amplifier, and eventually the output P44 of the AC amplifier becomes a voltage change that drops below the normal voltage level and returns to the original level. At this time, when the voltage of the output P44 becomes equal to or lower than the threshold value Vth3, the output P46 having a predetermined width is obtained at the second output circuit. As with the first embodiment, the circuit constants are set so that the voltage change of P44 falls between the threshold values Vth2 and Vth3 with respect to the slow change of the ambient environment, so that the outputs P45 and P46 do not change.

In FIG. 4, the output P set by the output P45 and reset by the output P46.
A third output circuit 11 having 47 (OUT3) (for example, a set-reset flip-flop circuit) may be provided, and a signal is continuously output while an object is in a proximity state like a conventional object detection device. You can

In the above embodiment, the output OUT
1, OUT2, and OUT3 can form an actual device alone or in any combination.

FIG. 6 is a circuit block diagram of the third embodiment.
FIG. 7 shows a timing chart of the voltage waveform of the main part.
6, those parts which are the same as those corresponding parts in FIG. 4 are designated by the same reference numerals.

In FIG. 6, 64 is a first integrator circuit comprising a resistor R61 and a capacitor C61, and 65 is a resistor R.
The second integrating circuit is composed of 62 and the capacitor C62, and the second integrating circuit has a larger integration constant than the first integrating circuit. In the embodiment, the resistors R61 and R62 have the same resistance value, and the capacitors C61 to C6
The capacitance of 2 is increased. The amplifier Q61, the resistor R63, and the capacitor C63 form a differential amplifier. Further, the output discriminating circuit 62 is composed of the first and second integrating circuits and the differential amplifier.

Now, when the object approaches the sensor electrode 5 of the converter 4 (point tA in FIG. 7), the capacitance of the converter 4 changes, and the duty ratio of the pulse of the output P41 of the oscillator 41 decreases. The output P41 of the oscillator 41 is connected to the first and second integration circuits, and the reduction of the duty ratio is converted into the reduction of the voltage by the integration circuit. Due to the difference in the integration constant, the output P62 is time Δt1 as shown by ΔP in FIG.
However, the output P63 becomes a steady value at time Δt2, and the voltage of the waveform P63 is higher than the voltage of the waveform P62. On the contrary, when the object is separated (point tB in FIG. 7),
A state occurs in which the voltage of the waveform P63 is lower than the voltage of the waveform P62. When there is no approach or separation of an object, or when the change due to environmental changes is gradual, the outputs of the above two integrating circuits are substantially equal or have a slight difference, and the output fluctuation of the differential amplifier is also slight. As a result, the output P64 of the differential amplifier changes like P64 shown in FIG. Thereafter, similarly to the second embodiment, an output is obtained when an object approaches or leaves the OUT1 and OUT2 terminals.

The oscillator circuit is not limited to the one described above, and the converter 4
Can be connected, and the output can be changed by the change in capacitance.The output discriminator does not change the output when the output change of the oscillator is relatively slow, and the output change of the oscillator If is relatively fast, it is sufficient if the output is changed significantly.

The output circuit is only required to be able to convert the output of the output discriminating circuit into a pulse having a predetermined voltage or current and a predetermined width, and a circuit for prohibiting the output when the power is turned on may be added. .

[0045]

According to the configuration of the present invention, when an object approaches or leaves the detection range of the object detection device at a predetermined speed, or when there is a rapid change in the state of passing the detection range. Only the output appears at the output terminal and does not appear even if there is a gradual change in the state. Normally, changes in temperature and humidity are slower than changes in the proximity of an object, and an object detection device that is not affected by changes in temperature and humidity can be configured.

Further, by setting appropriate circuit constants, it is possible to construct an object detecting device that does not malfunction even if dew condensation occurs due to a sudden change in temperature or humidity.

Further, it is possible to detect whether the object is close to or far from the object detecting device.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of an example of the present invention.

FIG. 3 is a timing chart showing the operation of the first embodiment of the present invention.

FIG. 4 is a circuit block diagram showing a second embodiment of the present invention.

FIG. 5 is a timing chart showing the operation of the second embodiment of the present invention.

FIG. 6 is a circuit block diagram showing a third embodiment of the present invention.

FIG. 7 is a timing chart showing the operation of the third embodiment of the present invention.

[Explanation of symbols]

 1, 41 Oscillator 2, 42, 62 Output discrimination circuit 3 Output circuit 4 Capacitance change type converter 5 Sensor electrode 6 Shield case 7 Object 8 Case 9 Back cover 10 Circuit board 11 Third output circuit 43 First output circuit 44 Second output circuit

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[Procedure amendment]

[Submission date] October 7, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG.

Claims (3)

[Claims] 1. An oscillator including a capacitance change type converter including a sensor electrode and a shield case, the output of which changes in response to a change in capacitance due to proximity or separation of an object, and an output change rate of the oscillator having a predetermined value. An object having an output discrimination circuit whose output does not change in response to the following changes and whose output changes in response to changes exceeding a predetermined value, and an output circuit which converts the output of the output discrimination circuit into a predetermined output Detection device. 2. A first output circuit which generates a predetermined output pulse when the proximity of an object is detected, and a second output circuit which generates a predetermined output pulse when the separation of an object is detected. Item 1. The object detection device according to item 1. 3. The object detection device according to claim 1, further comprising a third output circuit that generates an output pulse that rises when the proximity of an object is detected and falls when the separation of the object is detected. .